1. Field of the Invention
The present invention relates to certain novel silica catalysts comprising fluorine values, to a process for the preparation of such silica catalysts, and to the use thereof in the preparation of aromatic or aliphatic nitriles from corresponding formanilides, formamides or amides.
2. Description of the Prior Art
It is known to this art, from French Pat. No. 952,192, to prepare a silica containing fluorine and sodium values from sodium silicate. According to the particular process described therein, dissolved sodium silicate is added to a solution of excess sulfuric acid, and thereafter potassium fluoride is introduced thereto. Stated differently, over the course of the process, the formation of the silica is initially assisted by the reaction of sulfuric acid with sodium silicate, then the excess sulfuric acid reacts with the potassium fluoride subsequently introduced to yield hydrofluoric acid, which acid then impregnates the silica sol formed. In this manner, a silica is obtained which contains fluorine (the fluorine is essentially in the form of potassium fluorosilicate) and the specific surface of which is never less than 450 m.sup.2 /g, but often greater than 600 m.sup.2 /g, with a pore volume of about 80 cm.sup.3 /100 g, and with the average diameter of the pores ranging from about 60 to about 90 .ANG..
And per the aforecited patent, the product silica is useful as catalyst for such processes as cracking, reforming, isomerization, polymerization and alkylation.